a) Rubber is an insulator and does not conduct electricity. As such, its placement around the metal rods prevents the metal rods from touching each other or the metal container, ensuring that the pump is activated only when the metal sheet touches the rods (when the water level has risen to a certain height).
b) When it rains heavily, water will be collected in the metal container. As more water is collected, the water level will rise and bring the metal sheet (buoyant because of the wooden block below it) towards the metal rods. When the water level has risen to a certain height, the metal sheet will connect the metal rods, resulting in a closed circuit, thereby acting as a switch to turn on the pump.
c) We can dig a bigger hole at G. A bigger hole will allow more rainwater to be collected in the metal container even when it rains less heavily. This way, the water level will still rise to an enough height for the metal sheet to touch the metal rods.